Unit 10 - ElectricityUnit 10 - Electricity

What is electricity?What is electricity?

Electricity – form of energy caused by Electricity – form of energy caused by moving electronsmoving electrons

The AtomThe Atom

the atom has three basic partsthe atom has three basic parts

– ProtonProton

– NeutronNeutron

– ElectronElectron

The AtomThe Atom

the the protonsprotons and and neutronsneutrons are found in the are found in the nucleusnucleus

the the electronselectrons are found in a cloud around are found in a cloud around the nucleusthe nucleus

The AtomThe Atom

Protons have a positive (+) chargeProtons have a positive (+) charge

Electrons have a negative (-) chargeElectrons have a negative (-) charge

Neutrons are neutralNeutrons are neutral

The AtomThe Atom

objects with the same charge repel, or objects with the same charge repel, or move away from, each othermove away from, each other

objects with different charges attract each objects with different charges attract each otherother

most objects are electrically neutralmost objects are electrically neutral

The AtomThe Atom

Electrons can move from place to placeElectrons can move from place to place

Electrons always move from a Electrons always move from a negativelynegatively charged area to a charged area to a positivelypositively charged area charged area

this movement of electrons is the basis of this movement of electrons is the basis of electricityelectricity

Insulators & ConductorsInsulators & Conductors

Conductors – materials that allow electric Conductors – materials that allow electric charges to flow through them easilycharges to flow through them easily

Insulators & ConductorsInsulators & Conductors

some conductors are better than otherssome conductors are better than others

most metals are good conductors of most metals are good conductors of electricityelectricity

Insulators & ConductorsInsulators & Conductors

Insulators – materials that prevent electric Insulators – materials that prevent electric charges from flowing through them easilycharges from flowing through them easily

Insulators & ConductorsInsulators & Conductors

some examples of insulators include:some examples of insulators include:

– rubberrubber– corkcork– woodwood– plasticplastic

Insulators & ConductorsInsulators & Conductors

electric wires use both insulators and electric wires use both insulators and conductorsconductors– a conductor, often a copper wire, is coated a conductor, often a copper wire, is coated

with an insulator, such as rubberwith an insulator, such as rubber

– if the insulator wears out and the wires come if the insulator wears out and the wires come in contact, a in contact, a short circuitshort circuit occurs, allowing the occurs, allowing the electricity to jump between the wireselectricity to jump between the wires

Electric CurrentElectric Current

electric current – flow of electrons through electric current – flow of electrons through a conductora conductor

the number of electrons flowing the number of electrons flowing determines the amount of electric currentdetermines the amount of electric current

there are two types of electric current:there are two types of electric current:– Direct CurrentDirect Current– Alternating CurrentAlternating Current

Electric CurrentElectric Current

direct current – current in which electrons direct current – current in which electrons always flow in the same directionalways flow in the same direction

– current always flows from the current always flows from the negativenegative pole to pole to the the positivepositive pole pole

– all batteries provide direct currentall batteries provide direct current

Electric CurrentElectric Current

alternating current – current in which alternating current – current in which electrons change direction electrons change direction at a regular at a regular raterate

– most electricity that is used in everyday life most electricity that is used in everyday life comes from alternating currentcomes from alternating current

Electric CurrentElectric Current

– alternating current produces less heat, when alternating current produces less heat, when carried by wires from power plants, then direct carried by wires from power plants, then direct currentcurrent

this results in less damage to power cablesthis results in less damage to power cables

BatteriesBatteries

battery – series of electrochemical cells battery – series of electrochemical cells connected togetherconnected together

electrochemical cell – device that changes electrochemical cell – device that changes chemical energy into electrical energychemical energy into electrical energy

– a battery is a source of direct currenta battery is a source of direct current

BatteriesBatteries

when you connect the negative and when you connect the negative and positive poles of a battery to a conductor, positive poles of a battery to a conductor, electric current flows through the electric current flows through the conductorconductor

BatteriesBatteries

there are two types of batteries:there are two types of batteries:

– wet cellswet cells

– dry cellsdry cells

BatteriesBatteries

the simplest type of electrochemical cell is the simplest type of electrochemical cell is called a called a wet cellwet cell

a wet cell has three parts:a wet cell has three parts:– negative polenegative pole– positive polepositive pole– electrolyteelectrolyte

BatteriesBatteries

electrode – positive or negative pole of an electrode – positive or negative pole of an electrochemical cellelectrochemical cell

– the negative electrode is often made of the negative electrode is often made of zinczinc

– the positive electrode is often made of the positive electrode is often made of coppercopper

BatteriesBatteries

electrolyte – substance that dissolves in electrolyte – substance that dissolves in water to form a conducting solutionwater to form a conducting solution

– sulfuric acidsulfuric acid is often used as an electrolyte is often used as an electrolyte

BatteriesBatteries

a chemical reaction in the wet cell causes a chemical reaction in the wet cell causes electrons to build up on the zinc electrodeelectrons to build up on the zinc electrode

when the two electrodes are connected by when the two electrodes are connected by wire, electrons flow from the zinc to the wire, electrons flow from the zinc to the copper electrodecopper electrode

BatteriesBatteries

the most familiar type of electrochemical the most familiar type of electrochemical cell is called a cell is called a dry celldry cell

– a dry cell works the same way as a wet cell a dry cell works the same way as a wet cell with a with a positive electrodepositive electrode, a , a negative negative electrodeelectrode, and an , and an electrolyteelectrolyte

BatteriesBatteries

the electrolyte is a the electrolyte is a moist pastemoist paste inside the inside the cellcell

the negative electrode is the outside case the negative electrode is the outside case of the battery which is usually made of of the battery which is usually made of zinczinc

the positive electrode is located inside the the positive electrode is located inside the battery and is sometimes made of battery and is sometimes made of carboncarbon

BatteriesBatteries

newer style dry cell batteries use newer style dry cell batteries use nickel nickel oxideoxide for a positive electrode and for a positive electrode and cadmiumcadmium for a negative electrode for a negative electrode

– these are called nickel-cadmium, or ni-cad, these are called nickel-cadmium, or ni-cad, batteriesbatteries

Electric CircuitsElectric Circuits

electric circuit – path that an electric electric circuit – path that an electric current followscurrent follows

all electric circuits have three partsall electric circuits have three parts– source of electric currentsource of electric current– load (something that uses electricity)load (something that uses electricity)– wires (connect the source to the load)wires (connect the source to the load)

most electric circuits also have a switchmost electric circuits also have a switch

Electric CircuitsElectric Circuits

there are two types of electric circuitsthere are two types of electric circuits

– series circuitseries circuit

– parallel circuitparallel circuit

Electric CircuitsElectric Circuits

series circuit – circuit in which electric series circuit – circuit in which electric current follows only one pathcurrent follows only one path

– a series circuit is the simplest type of electric a series circuit is the simplest type of electric circuitcircuit

Electric CircuitsElectric Circuits

parallel circuit – circuit in which electrical parallel circuit – circuit in which electrical current can follow more than one pathcurrent can follow more than one path

– if several appliances are connected in a if several appliances are connected in a parallel circuit, current can still reach the other parallel circuit, current can still reach the other appliances if one of them stops workingappliances if one of them stops working

– parallel circuits are used in homes, schools, parallel circuits are used in homes, schools, and office buildingsand office buildings

Volts, Amps, & OhmsVolts, Amps, & Ohms

electromotive force – force that makes electromotive force – force that makes electrons moveelectrons move

– electromotive force is abbreviated EMFelectromotive force is abbreviated EMF

Volts, Amps, & OhmsVolts, Amps, & Ohms

volt – unit used to measure volt – unit used to measure electromotive electromotive forceforce

– voltage is measured with a voltmetervoltage is measured with a voltmeter

Volts, Amps, & OhmsVolts, Amps, & Ohms

ampere – unit used to measure electric ampere – unit used to measure electric currentcurrent

– one ampere, or one ampere, or ampamp, is the amount of current , is the amount of current passing a point each secondpassing a point each second

Volts, Amps, & OhmsVolts, Amps, & Ohms

the amount of electric current depends on the amount of electric current depends on the number of electrons flowing in a circuitthe number of electrons flowing in a circuit

current is measured with an current is measured with an ammeterammeter

Volts, Amps, & OhmsVolts, Amps, & Ohms

as current flows through a wire, it meets as current flows through a wire, it meets resistanceresistance from the wire from the wire

Volts, Amps, & OhmsVolts, Amps, & Ohms

resistance – opposition to the flow of resistance – opposition to the flow of electric currentelectric current

Ohm – unit used to measure resistanceOhm – unit used to measure resistance

Volts, Amps, & OhmsVolts, Amps, & Ohms

resistance of a wire depends on:resistance of a wire depends on:

– lengthlength

– thicknessthickness

– materialmaterial

– temperaturetemperature

Volts, Amps, & OhmsVolts, Amps, & Ohms

length – the longer a wire is, the more length – the longer a wire is, the more resistance it hasresistance it haswidth – the thinner a wire is, the more width – the thinner a wire is, the more resistance it hasresistance it hasmaterial – wires made of poor conductors material – wires made of poor conductors have more resistance than wires made of have more resistance than wires made of good conductorsgood conductorstemperature – as a wire gets hotter, its temperature – as a wire gets hotter, its resistance increasesresistance increases

Volts, Amps, & OhmsVolts, Amps, & Ohms

every closed circuit has:every closed circuit has:

– current (I)current (I)

– voltage (V)voltage (V)

– resistance (R)resistance (R)

Volts, Amps, & OhmsVolts, Amps, & Ohms

different power sources have different different power sources have different amounts of amounts of voltagevoltage

the the resistanceresistance varies depending on the varies depending on the type of wires usedtype of wires used

the the currentcurrent is affected by the is affected by the voltagevoltage and and the the resistanceresistance

Ohm’s LawOhm’s Law

Ohm’s law – current in a wire is equal to Ohm’s law – current in a wire is equal to the voltage divided by the resistancethe voltage divided by the resistance

– current = voltage / resistancecurrent = voltage / resistance

I = V/RI = V/R

Ohm’s LawOhm’s Law

Voltage(V)

Current(I)

Resistance(R)

Electric SafetyElectric Safety

too much current in a circuit can cause an too much current in a circuit can cause an overloaded circuitoverloaded circuit

electric current comes into a house from electric current comes into a house from power lines to a breaker boxpower lines to a breaker box

Electric SafetyElectric Safety

breaker boxes contain:breaker boxes contain:

– fusesfuses

oror– circuit breakerscircuit breakers

Electric SafetyElectric Safety

fuse – wire that melts and breaks a circuit fuse – wire that melts and breaks a circuit if too much current is flowingif too much current is flowing

– by melting, the fuse stops current from flowing by melting, the fuse stops current from flowing and prevents an overloaded circuitand prevents an overloaded circuit

– fuses need to be replaced when they become fuses need to be replaced when they become overloadedoverloaded

– fuses are used in many older homesfuses are used in many older homes

Electric SafetyElectric Safety

circuit breaker – switch that opens a circuit circuit breaker – switch that opens a circuit if too much current is flowingif too much current is flowing

– a circuit breaker can be reset when it a circuit breaker can be reset when it becomes overloadedbecomes overloaded

– most newer homes have circuit breakersmost newer homes have circuit breakers